Plant nutrient coated nanoparticles and methods for their preparation and use

ABSTRACT

Embodiments described herein provide for nanofertilizers having at least one plant nutrient coated onto a metal nanoparticle. Some embodiments provide for a method of making a nanofertilizer including providing a metal nanoparticle and coating the metal nanoparticle with at least one plant nutrient or precursor thereof. In some embodiments, a method of making a nanofertilizer may include mixing a metal salt and a plant nutrient in an aqueous medium to form a solution and adding a reducing agent to the solution to form a coated metal nanoparticle. Some embodiments provide for a boron nanofertilizer and methods of making the same. Some embodiments provide for a method of treating a plant nutrient deficiency, such as, for example, a boron deficiency. Some embodiments also provide for a kit for making a plant nutrient coated nanoparticle.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application of U.S. patentapplication Ser. No. 13/825,661, filed on Mar. 22, 2013, entitled “PlantNutrient Coated Nanoparticles And Methods For Their Preparation AndUse,” which is a U.S. national stage filing under 35 U.S.C. §371 ofInternational Application No. PCT/IB2012/001511, filed on Aug. 7, 2012,entitled “Plant Nutrient Coated Nanoparticles And Methods For TheirPreparation And Use,” which claims benefit of and priority to IndianApplication No. 154/KOL/2012, filed on Feb. 15, 2012. The contents ofeach of these applications are incorporated herein by reference in theirentireties.

BACKGROUND

Plants require certain essential nutrients for normal functioning andgrowth. Nutrient levels outside the amount required for normalfunctioning and growth may cause overall crop growth and health todecline due to either a deficiency or a toxicity. Nutrient deficiencyoccurs when an essential nutrient is not available in sufficientquantity to meet the requirements of a growing plant. Toxicity occurswhen a nutrient is in excess of plant needs and decreases plant growthor quality.

Plant nutrients are divided into two categories: macronutrients, whichare consumed in larger quantities and may be present in plant tissue inquantities from about 0.2% to about 4.0% by dry matter weight; andmicronutrients, which are consumed in smaller quantities and may rangefrom about 5 parts per million (ppm) to about 200 ppm or less than about0.2% dry weight. Macronutrients include carbon, hydrogen, oxygen,phosphorus, potassium, nitrogen, sulfur, calcium, magnesium, andsilicon. Micronutrients include iron, molybdenum, boron, copper,manganese, sodium, zinc, nickel, chlorine, selenium, vanadium andcobalt.

There are three fundamental ways plants uptake nutrients through theroot: (1) simple diffusion, where a nonpolar molecule, such as, forexample, O₂, CO₂, and NH₃ that follow a concentration gradient, canpassively move through the lipid bilayer membrane without the use oftransport proteins; (2) facilitated diffusion, where the rapid movementof solutes or ions following a concentration gradient is facilitated bytransport proteins; and (3) active transport, in which the activetransport of ions or molecules against a concentration gradient requiresan energy source, usually ATP, to pump the ions or molecules through themembrane.

However, not all plant nutrients are equally mobile. For example, boronis generally considered to be phloem immobile or to have only limitedphloem mobility in higher plants. The mobility of boron from outside theplant cell to inside the plant cell typically involves mediation by aboron polyol complex. Polyol compounds, however, may not be presentsufficiently or may be totally absent in higher plants. Thus, in mostcommercial field crops and horticultural crops (which lack polyol),boron's mobility is restricted and boron fertilization is limited. Thus,there is a need for a more mobile and efficient nutrient fertilizationmethod in plants.

SUMMARY

Some embodiments described in this document relate to a nanofertilizerincluding at least one plant nutrient coated onto a metal nanoparticle.In some embodiments, the at least one plant nutrient includes nitrogen,phosphorous, potassium, calcium, sulfur, magnesium, boron, copper, iron,chloride, manganese, molybdenum, zinc, a precursor thereof or acombination thereof. In some embodiments, the at least one plantnutrient includes boron, boric acid, disodium octaborate tetrahydrate,calcium borate, magnesium borate, sodium borosilicate, sodiumtetraborate decahydrate, sodium borate, sodium tetraborate, disodiumtetraborate or a combination thereof. In some embodiments, the metalnanoparticle includes gold, silver, copper, aluminum, nickel, chromium,iron, cobalt, tin, titanium, silicon, zinc, lead, platinum, palladium,rhodium, tantalum, ruthenium, tungsten, an alloy thereof or acombination thereof.

Some embodiments described in this document relate to a method of makinga nanofertilizer which includes providing a metal nanoparticle; andcoating the metal nanoparticle with at least one plant nutrient or aplant nutrient precursor. In some embodiments, providing the metalnanoparticle includes forming the metal nanoparticle through saltreduction synthesis, reverse micelles process, microwave dielectricheating reduction, ultrasonic irradiation, radiolysis, solvothermalsynthesis, bioreduction, heat evaporation, photochemical reduction,electrochemical synthesis, or a combination thereof.

Some embodiments described in this document relate to a method of makinga nanofertilizer which includes mixing a metal salt and a plant nutrientin an aqueous medium to form a solution; and adding a reducing agent tothe solution to form a coated metal nanoparticle. In some embodiments,the reducing agent is added to the solution in a dropwise manner. Insome embodiments, the reducing agent includes sodium citrate, sodiumborohydride, hydroquinone, glycol ethylene, formaldehyde, ethanol,hydroxyl radicals, sugar pyrolysis radicals, hydrazine hydrate,saccharide, N,N-dimethylformamide or a combination thereof.

In some embodiments, the method also includes heating the solutionbefore adding the reducing agent. The solution may be heated to atemperature of about 70° C. to about 110° C. In some embodiments, themethod also includes adding a stabilizer to the solution after addingthe reducing agent. The stabilizer may include polyvinyl alcohol,polyethylene glycol, carboxymethyl cellulose, poly(vinylpyrrolidone),sodium dodecyl sulphate, long-chain thiol, long-chain amines, carboxyliccompounds, bovine serum albumin, citrate, cellulose, or a combinationthereof.

Some embodiments described in this document relate to a method of makinga boron nanofertilizer, the method comprising adding silver nitrate andboric acid to an aqueous medium to form a solution; and adding areducing agent to the solution to form a boric acid coated silvernanoparticle. In some embodiments, the reducing agent includes sodiumcitrate. In some embodiments, the aqueous medium includes water.

Some embodiments described in this document relate to a method fortreating boron deficiency in a plant comprising administering a metalnanoparticle coated with boron or a precursor thereof to the plant. Insome embodiments, the coated metal nanoparticle is administered as aspray, hydroponics, aeroponics, seed treatment, seedling root dipping,soil application, nutrient for tissue culture, in vitro culture,application with irrigation water or a combination thereof. The coatedmetal nanoparticle may be administered in an amount effective to treatboron deficiency. The coated metal nanoparticle may be administered inan amount without causing boron toxicity.

Some embodiments described in this document relate to a kit for making aplant nutrient coated metal nanoparticle which includes a metal salt; aplant nutrient; and a reducing agent. The kit may also include anaqueous medium. In some embodiments, the kit also includes a deliveryapparatus to deliver the plant nutrient coated metal nanoparticle to aplant. In some embodiments, the delivery apparatus is a sprayingapparatus.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates transmission electron microscopy images of boric acidcoated silver nanoparticles at different stages of release of boric acidfrom the surface of silver nanoparticles.

FIG. 2 illustrates phase contrast microscopic images of (a) boric acidcoated silver nanoparticle absorption through leaf epidermis; (b), (c),(d), (e), (f) transport of boric acid coated silver nanoparticle throughvascular bundles at different stages.

FIG. 3 illustrates penetration of boric acid coated silver (Ag—B) coreshell nanoparticles across leaf cuticle, stomata and potato leaves.

FIG. 4 illustrates a comparison between an Ag—B nanoparticle treatedleaf (left—dark green) and a leaf treated with macro-boric acid(right—lighter green).

FIG. 5 illustrates Ag—B nanofertilizer concentrations and macro-boricacid concentrations in various treatments.

FIG. 6 illustrates boron concentration in leaf at different growthstages sprayed with Ag—B nanofertilizers (A) and boron concentration inleaf and stem (just 1 cm above root) during various growth stages (B).

FIG. 7 illustrates that a trace amount of boron (<2 ppm) has been foundin tubers under all treatments.

FIG. 8 illustrates chlorophyll a and chlorophyll b content in potatoleaves measured at 15 (A) and 30 (B) days after spraying Ag—Bnanofertilizer.

FIG. 9 illustrates total plant weight (aerial part), total tuber yieldand total biomass of potato under various concentrations of Ag—Bnanofertilizers (q-ha=quintals/hectare).

FIG. 10 illustrates dry weight of tubers per 100 grams of fresh weight,ash content (percentage) of leaf and stem of Ag—B nanofertilizer treatedpotato plants.

FIG. 11 illustrates biochemical analysis of potato tubers for starch,soluble sugar, reducing sugar content after 30 days in cold storage.

FIG. 12 illustrates a solution of silver nanoparticles stabilized bysodium dodecyl sulphate (SDS) (left) and a solution of silver particlescoated with boric acid (right).

FIG. 13A and FIG. 13B illustrate UV-VIS spectra of (A) silvernanoparticles stabilized by SDS and (B) Ag—B nanoparticles.

FIG. 14 illustrates transmission electron microscopy images of silvernanoparticles stabilized with sodium dodecyl sulphate (SDS) (upper) andAg—B nanoparticles (lower).

FIG. 15 illustrates the particle size distribution of Ag—B NP from Zetaanalyzer.

FIG. 16 illustrates a potato leaf sprayed with Ag—B nanofertilizer(left) and a leaf sprayed with macro boric acid (right).

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part of this document. In thedrawings, similar symbols typically identify similar components, unlessthe context dictates otherwise. The illustrative embodiments describedin the detailed description, drawings, and claims are not meant to belimiting. Other embodiments may be used, and other changes may be made,without departing from the spirit or scope of the subject matterpresented in this document. It will be readily understood that theaspects of the present disclosure, as generally described in thisdocument, and illustrated in the Figures, can be arranged, substituted,combined, separated, and designed in a wide variety of differentconfigurations, all of which are explicitly contemplated to be withinthe scope of this disclosure.

Some embodiments are directed to plant nutrient coated metalnanoparticles and methods of making and using such nanoparticles.Nanoparticles are capable of penetrating living plant tissues andmigrating to different regions of the plant. Use of such nanoparticlesfor nanofertilization may transport the plant nutrient to the plant cellplasma membrane, without the need for any additional energy and exhibitsno phytotoxicity. The coated metal nanoparticle may be capable oftransport across a plant membrane system without mediation of complexpolysaccharides and without ATP energy from the plant. The coated metalnanoparticle may be used as a foliar spray, seed treatment, rootdipping, soil application in precision farming, glass house farming,applying with irrigation water and as plant nutrient in tissue cultureor any in vitro culture media for micropropagation and regeneration ofplants.

Some embodiments disclosed in this document relate to a nanofertilizerincluding at least one plant nutrient coated onto a metal nanoparticle.The nanofertilizer may be in an aqueous solution. Owing to a highsurface area to volume ratio, the effectiveness of such nanofertilizersmay surpass the most innovative polymer-coated conventional fertilizers,which have seen little improvement in the past ten years.

Some embodiments relate to a method of making a nanofertilizer includingthe steps of providing a metal nanoparticle and coating the metalnanoparticle with at least one plant nutrient or a precursor thereof.Providing the metal nanoparticle may include forming the metalnanoparticle through salt reduction synthesis, reverse micelles process,microwave dielectric heating reduction, ultrasonic irradiation,radiolysis, solvothermal synthesis, bioreduction, heat evaporation,photochemical reduction, electrochemical synthesis, or a combinationthereof.

The at least one plant nutrient of embodiments herein may includenitrogen, phosphorous, potassium, calcium, sulfur, magnesium, boron,copper, iron, chloride, manganese, molybdenum, zinc, a precursor thereofor a combination thereof. In some embodiments, the plant nutrient may beboron, boric acid, disodium octaborate tetrahydrate, calcium borate,magnesium borate, sodium borosilicate, sodium tetraborate decahydrate,sodium borate, sodium tetraborate, disodium tetraborate or a combinationthereof. In some embodiments, the plant nutrient may include lime,gypsum, superphosphate, iron sulfate, iron chelate, ferritin, zincoxide, zinc sulfate, zinc chelate, potassium nitrate, calcium nitrate,magnesium nitrate, monoammonium phosphate, ammonium sulfate, magnesiumsulfate, monopotassium phosphate, calcium carbonate, ammonium nitratesulfate, ammonium thiosulfate, aqua ammonia, calcium cyanamide,crotonylidene diurea, diacyandiamide, isobutylidene diurea, sodiumnitrate, potassium carbonate, potassium chloride, potassium magnesiumsulfate, potassium metaphosphate, potassium sulfate, calcium chloride,calcium oxide, calcitic limestone, dolomitic limestone, magnesiumammonium phosphate, magnesium oxide, copper chelates, cupric ammoniumphosphate, copper sulfate, copper frits, copper polyflavonoid,malachite, azurite, cuprous oxide, cupric oxide, cupric acetate, boricacid, sodium tetraborate, sodium tetraborate decahydrate, boron frit,sodium borosilicate, calcium borate, magnesium borate, sodium borate,disodium octaborate tetrahydrate, disodium tetraborate, ferric sulfate,ferrous sulfate, ferrous ammonium sulfate, ferrous ammonium phosphate,ferrous oxalate, ferrous carbonate, iron chelate, iron lignosulfonate,iron polyflavonoid, iron frits, iron methoxyphenylpropane, ferrousoxide, ferric oxide, iron ammonium polyphosphate, manganese oxide,manganese methoxyphenyl propane, manganese fits, manganese chloride,manganese carbonate, manganese sulfate, manganese chelate, manganeseammonium phosphate, manganese polyflavonoid, ammonium molybdate, sodiummolybdate, molybdenum fit, molybdenum trioxide, molybdenum sulfide, zincfrit, zinc carbonate, zinc phosphate, zinc ammonium phosphate, zincsulfide, zinc lignosulfonate, zinc polyflavonoid or a combinationthereof.

In some embodiments, the metal nanoparticle may include gold, silver,copper, aluminum, nickel, chromium, iron, cobalt, tin, titanium,silicon, zinc, lead, platinum, palladium, rhodium, tantalum, ruthenium,tungsten, an alloy thereof or a combination thereof. In particularembodiments, the nanoparticle may be silver. In some embodiments, thenanoparticle may be copper. In some embodiments, the nanoparticle may begold. In some embodiments, the nanoparticle may include a size of about1 nm to about 100 nm.

Some embodiments described in this document provide for a boronnanofertilizer including boron or a precursor thereof coated onto ametal nanoparticle. Boron is an element which plays a vital role invarious metabolic and biochemical activities in plants and animals.Boron is considered to be involved in nucleic acid metabolism,carbohydrate and protein metabolism, indole acetic acid metabolism, cellwall synthesis, cell wall structure, membrane integrity and function,and phenol metabolism; however, the molecular basis of these roles ismostly unknown.

It is believed that the boric acid nanoparticles of embodiments hereinmay be transported through the plant cell plasma membrane, without theneed for any additional energy, and exhibits no phytoxicity. Boric acidis a compound containing boron, hydrogen and oxygen in 3:1:3proportions.

Compared to the conventional boric acid or Borax fertilizers, all ofwhich are on the macro scale (on the order of micrometers) (“macro boricacid”), the boron nanofertilizer of embodiments herein (on the order ofnanometers) shows a sharp increase in crop yield (increased biomass,potato tuber yield, and plant weight) and crop quality (less reducingsugar and increased starch content). Accordingly, one benefit of theboron nanofertilizer described in embodiments may be extremely low costand high efficiency. Some embodiments described herein provide a highlyeffective means of nanofertilization by administration of boric acidnanoparticles to plants. Nanoscale boric acid released from the surfaceof metal nanoparticles of embodiments herein can be a highly efficientboron fertilizer. Other benefits of the boron coated metal nanoparticlesdescribed herein include increased boron content in plants resulting inincreased chlorophyll content, number of leaves, total biomass, totalyield, and lowered soluble and reducing sugars.

Some embodiments relate to a method of making a nanofertilizer includingthe steps of mixing a metal salt and a plant nutrient in an aqueousmedium to form a solution; and adding a reducing agent to the solutionto form a coated metal nanoparticle. In some embodiments, the reducingagent may be added to the solution in a dropwise manner.

In some embodiments, the metal salt includes a metal selected from gold,silver, copper, aluminum, nickel, chromium, iron, cobalt, tin, titanium,silicon, zinc, lead, platinum, palladium, rhodium, tantalum, ruthenium,tungsten, an alloy thereof or a combination thereof. In someembodiments, the metal salt includes a salt selected from a chloride,fluoride, acetate, sulfate, nitrate, carbonate, nitrite, citrate,cyanide, hydroxide, oxide, phosphate or a combination thereof. Inparticular embodiments, the salt may be silver nitrate. In someembodiments, the salt may be copper sulfate. In some embodiments, thesalt may be gold chloride. In some embodiments, the aqueous medium maybe water.

In some embodiments, the reducing agent comprises sodium citrate, sodiumborohydride, hydroquinone, glycol ethylene, formaldehyde, ethanol,hydroxyl radicals, sugar pyrolysis radicals, hydrazine hydrate,saccharide, N,N-dimethylformamide or a combination thereof. In someembodiments, the reducing agent may be sodium citrate. In someembodiments, the reducing agent may be sodium borohydride.

The solution may be heated before adding the reducing agent. In someembodiments, the solution may be further heated to a temperature ofabout 70° C. to about 110° C. before adding the reducing agent. Inembodiments, the solution may be heated to a temperature of about 70° C.to about 100° C., about 70° C. to about 95° C., about 70° C. to about90° C., about 70° C. to about 85° C., about 75° C. to about 110° C.,about 75° C. to about 100° C., about 75° C. to about 95° C., about 75°C. to about 90° C., about 75° C. to about 85° C., about 80° C. to about110° C., about 80° C. to about 100° C., about 80° C. to about 95° C.,about 80° C. to about 90° C., about 80° C. to about 85° C., acombination thereof or the like. Specific examples include about 70° C.,about 75° C., about 80° C., about 85° C., about 90° C., about 95° C.,about 100° C., and ranges between any two of these values.

In some embodiments, a stabilizer may be added to the solution afteradding the reducing agent. The stabilizer may include polyvinyl alcohol,polyethylene glycol, carboxymethyl cellulose, poly(vinylpyrrolidone),sodium dodecyl sulphate, long-chain thiol, long-chain amines, carboxyliccompounds, bovine serum albumin, citrate, cellulose, or a combinationthereof.

Some embodiments of this document provide for the synthesis of boricacid coated metal core shell nanoparticles (NP), their delivery intoplants, and smart uptake by a non-mediated transport through the plasmamembrane into the cell without making a polyol complex. It is believedthat two types of compounds with polyols are formed in solutions ofboric acid. See Raven J A (1980) Short- and long-distance transport ofboric acid in plants, New Phytologist 84: 231-249 and Rowe R I, EckhertC D (1999) Boron is required for zebrafish embryogenesis, J Exp Bot202:1649-1654. As seen in FIG. 4, the metal nanoparticles (left side)act as catalysts for movement of nanofabricated plant nutrients acrossthe cell membrane.

Some embodiments provide for a method of making a boron nanofertilizerincluding adding a metal salt and boric acid to an aqueous medium toform a solution; and adding a reducing agent to the solution to form aboric acid coated metal nanoparticle.

In some embodiments, nanofabrication of essential plant nutrientnanofertilizer and its application methods may be achieved at very lowdoses. In some embodiments, the concentration of boron in thenanofertilizer may be about 1/100000^(th) or less than the boronconcentration of the conventional macro boric acid solution, and mayresult in as much as a 111% increase in potato tuber yield. In someembodiments, the boron concentration in the nanofertilizer may be about0.001 ppm to about 2.0 ppm, about 0.001 ppm to about 1.5 ppm, 0.001 ppmto about 1.0 ppm, 0.001 ppm to about 0.5 ppm, 0.001 ppm to about 0.1ppm, 0.001 ppm to about 0.05 ppm, about 0.01 ppm to about 2.0 ppm, about0.01 ppm to about 1.5 ppm, about 0.01 ppm to about 1.0 ppm, 0.01 ppm toabout 0.5 ppm, 0.01 ppm to about 0.1 ppm, 0.01 ppm to about 0.05 ppm, acombination thereof or the like. Specific examples, without limitation,of boron concentration in the nanofertilizer may include about 0.062ppm, about 0.0465 ppm, about 0.0300 ppm, about 0.0248 ppm, about 0.0186ppm, about 0.0124 ppm, about 0.0062 ppm, and ranges between any two ofthese values.

Some embodiments of this document also provide for a method of treatinga plant nutrient deficiency. In some embodiments, the method includesadministering a metal nanoparticle coated with at least one plantnutrient or a precursor thereof to the plant. In some embodiments, thecoated metal nanoparticle is administered in an amount such that it iseffective to treat the plant nutrient deficiency without causingtoxicity.

In some embodiments, the coated metal nanoparticle may be administeredas a spray, hydroponics, aeroponics, seed treatment, seedling rootdipping, soil application, tissue culture, in vitro culture, applicationwith irrigation water or a combination thereof. In some embodiments, thecoated metal nanoparticle is administered as a foliar spray.

Some embodiments are related to a kit for making a plant nutrient coatedmetal nanoparticle which includes a metal salt, a plant nutrient and areducing agent. The plant nutrient coated nanoparticle may be in anaqueous medium. In some embodiments, the kit may further include adelivery apparatus for delivering the plant coated metal nanoparticle tothe plant. In some embodiments, the delivery apparatus is a sprayingapparatus.

Example 1 Preparation of Boric Acid Coated Nanoparticle FertilizersUsing Sodium Citrate as a Reducing Agent

Silver-boric acid nanostructures were prepared in aqueous medium byreduction synthesis method. 100 mM AgNO₃ and 100 mM boric acid (H₃BO₃)stock solutions and 2% w/v dibasic sodium citrate solution wereprepared; 50 ml double distilled water was taken in 100 ml Erlenmeyerflask and heated while stirring near boiling ˜80° C. 500 μL of 100 mMAgNO₃ was added to it and heated to 80° C., and stirred for nearly 1minute. Then 500 μL of 100 mM boric acid solution was added to it. Thesolution was heated and stirred for 2 minutes. 2% w/v sodium citrate wasadded to the solution drop by drop. The solution was heated until thecolor change was evident (pale yellow).

Then the temperature was reduced and the solution was stirred for 50minutes to room temperature. The prepared transparent, pale yellowsolution was kept in the freezer for further characterization by UV-VISspectrophotometer (FIG. 13), Zeta analyzer (FIG. 15), transmissionelectron microscope (TEM) (FIG. 14). As shown in FIG. 14, the TEM imagesof the Ag—B nanoparticles show a visible coating of boric acid.

As shown in FIG. 1, the transmission electron microscopy imagesillustrated that the rate of release depends on various factors:concentration of boric acid as coating agent, total time and temperatureduring synthesis. The boric acid started releasing 24-48 hours afterspraying on foliage. Under normal temperature conditions, the coatednanoparticles may be stored for at least months.

As shown in FIG. 2 illustrating the phase contrast microscopy images, itis believed that the delivered nanofabricated boron nutrients aretransported through the plasma membrane of the plant cell by effusionrequiring no energy or minimal energy, not by diffusion. Boron is anessential plant nutrient but its mobility in plants is greatlyunresolved—although it is known that some plants are boron mobile andsome are extremely immobile causing acute boron deficiency disorders. Itis believed that the boric acid coated silver nanoparticles (size10-1000 nm) are able to readily transport across plant membrane systemwithout the mediation of complex polysaccharides, as required by macroboric acid treatment. FIGS. 3 and 4 illustrate the mode of transport ofnonpolar nutrient nanoparticles through the plant plasma membrane withno energy requirement from ATP in the cell. FIG. 3 illustrates thepenetration of boric acid coated silver core shell nanoparticles acrossleaf cuticle, stomata of potato plants. FIG. 4 illustrates thedifferences in membrane transport of boric acid coated silver (leftside) nanoparticles (which does not require polyol mediation) andmacro-size boric acid (right side) (which can't enter the cell withoutcomplexing with mannitol). It is believed that the metal nanoparticlesact as catalysts for movement of nanofabricated plant nutrients acrossthe plant cell membrane. As shown in FIG. 4, the potato leaf (left)treated with Ag—B nanoparticle (0.062 ppm concentration of nano boricacid treatment) is a deep green color compared to macro boric acid(6.2×10³ ppm concentration boric acid) sprayed on potato leaf (right).FIG. 4 clearly shows that a 100,000 times lower concentration ofnano-boric acid has a much higher efficacy than macro boric acid. (Seealso FIG. 8 on chlorophyll concentrations under different treatments).

Example 2 Preparation of Boric Acid Coated Nanoparticle FertilizersUsing Sodium Borohydride as a Reducing Agent

Silver-boric acid nanostructures were prepared in aqueous medium byreduction synthesis method. 500 μL of 100 mM AgNO₃ was added to 50 mldouble distilled water and heated to 80° C., and stirred for nearly 1minute. Then 500 μL of 100 mM boric acid solution was added to it. Thesolution was heated and stirred for 2 minutes. 0.75M sodium borohydridesolution was added to the solution drop by drop. The solution was heateduntil the color change was evident (pale yellow). Then the temperaturewas reduced and the solution was stirred for 50 minutes to roomtemperature. It was found that sodium borohydride reduced Ag—B showed notoxicity on treated rice plants (data not shown).

Example 3 Improved Crop Productivity from Application of Boric AcidNanoparticles

Boric acid coated silver nanoparticles (Ag—B NP) were applied to potatocrops as a foliar spray and, 45 days after spraying, the growthattributes, yield components, and quality parameters of the potato(Solanum tuberosum) crop were evaluated. A boric acid (BA) macroparticle spray (0.62% w/v), containing approximately 6.2×10³ ppm BA, andvarious concentrations of Ag—B nanoparticles (nanofertilizer) containing0.062 ppm, 0.0465 ppm, 0.0300 ppm, 0.0248 ppm, 0.0186 ppm, 0.0124 ppm,0.0062 ppm of boric acid were also evaluated (see Table 1 below). FIG. 5illustrates the different boric acid concentrations in the differentAg—B nanofertilizer treatments (T1-T7) as well as the macro boric acidconcentration (T8), silver nanoparticle (T9) and control (T10). Theboric acid removable coating on the silver nanoparticles eventuallyreleased from the surface of the silver nanoparticle inside the planttissue and boric acid was made available as nanonutrient to penetratedirectly into cell membrane without making a boron-polyol complex.

TABLE 1 Boric Acid (BA) Treatment conc. in spray Composition ParticleSize T1 0.062 ppm BA coated on Ag-NP <100 nm T2 0.0465 ppm BA coated onAg-NP <100 nm T3 0.03 ppm BA coated on Ag-NP <100 nm T4 0.0248 ppm BAcoated on Ag-NP <100 nm T5 0.0186 ppm BA coated on Ag-NP <100 nm T60.0124 ppm BA coated on Ag-NP <100 nm T7 0.0062 ppm BA coated on Ag-NP<100 nm T8 6200 ppm Macro BA >8000 nm  T9 0 ppm Only Silver NP <100 nm T10 0 ppm Control No B

Boric acid coated silver nanoparticles had significant effect on growthparameters like plant height, leaf numbers, chlorophyll content, totalbiomass, dry matter accumulation, fresh weight, tuber yield; along withquality parameters like decrease in soluble and reducing sugar, increasein starch and tuber ash percentage with nanofertilizer concentrations.As shown in FIG. 6, boron concentrations in leaf and tuber significantlyincreased when sprayed with Ag—B nanofertilizers compared to macro boricacid (T8). There was 100,000 times higher boron concentration in spraysolution than nanofertilizer. Ag—B nanofertilizer concentrations sprayedon foliage transported from leaves to stem and younger leaves. Within 15days of spraying almost 80% of boron transported from leaves to otherparts. At 30 days after spraying trace amount of boron was found in leafbut 90% of boron was found to be deposited in basal portion of stem (1cm above root level). Therefore, boron concentration in stem increasedwith a gradual decline in boron concentration in leaf (compare boronconcentrations at 30 days in leaf and stem in FIG. 6). A trace amount ofboron (<2 ppm) was found in potato tubers under all treatments as shownin FIG. 7.

As shown in FIG. 8, chlorophyll a content in Ag—B nanofertilizer treatedleaves increased at both stages of growth (15 days and 30 days), butmacro boric acid (T8) was as good as without treatment. Mostsignificantly, Ag—B nanofertilizer spray had reduced chlorophyll bcontent with increasing dose of nanofertilizer. As shown in FIG. 9, itis clearly visible that total plant weight (above ground), tuber yieldand total biomass were increased with nanofertilizer application. Macroboric acid (column T8 in FIG. 9) is no better than control (withoutspray). Similarly SDS stabilized silver nanoparticles may have no effecton the above parameters. All measured plant growth parameters, yieldattributes and quality parameters were significantly better with theAg—B nanofertilizer treatments. Furthermore, as seen in FIG. 16, potatoleaves sprayed with Ag—B nanofertilizer (left) showed a dark green,fleshy, undulated and hairy leaf in comparison with a macro boric acidsprayed potato leaf (right) which showed a light green colored leaf.When dry weight of tubers per 100 gm of fresh weight, ash content ofleaf and stem of Ag—B nanofertilizer treated potato plants wasdetermined, as shown in FIG. 10, it was determined that maximum tuberdry matter was found from T1 and T2 respectively. Biochemical analysisof potato tubers for starch, soluble sugar, reducing sugar content after30 days in cold storage, seen in FIG. 11, showed high starch and lowreducing sugar in Ag—B nanofertilizer treated potato samples (T1 only)whereas all other treatments were equivalent. However starch content wasincreased in all nanofertilizer treated samples.

Silver nanoparticles were synthesized using sodium dodecyl sulphate asstabilizer, which was also sprayed on the crop foliage (T9) at the timeof application of other treatments, but there was no detectable responseto silver nanoparticle coated with SDS. Therefore it is believed thatall effects produced by nanofertilizer were due to boric acid. As shownin FIG. 12, the color of Ag nanoparticles coated with boric acid is paleyellow (right side of FIG. 12) and lighter in color compared to Agnanoparticles stabilized by SDS (sodium dodecyl sulphate, left side ofFIG. 12). As the data presented above shows, the proposed Ag—Bnanofertilizer is unique and it increases the productivity of theresulting crop by at least 100 times and improves the quality (lessreducing sugar and increased starch content) of the produce.

Example 4 Preparation of Boric Acid Coated Nanoparticle FertilizersUsing Copper Sulfate as the Metal Salt

Copper-boric acid (Cu—B) nanostructures were prepared in aqueous mediumby reduction synthesis method. CuSO₄ was added to sodium borohydride atroom temperature and stabilized by polyvinylpyrrolidone(PVP) tosynthesize Cu—B nanoparticles.

Cu—B nanoparticles were sprayed on foliage at flowering stage of rice.Panicle weight, number of grains, and grain weight of treated plantswere recorded. Cu—B treated plants gave higher yield of rice thancontrol (data not shown). However, it is believed that because copper isalso a micronutrient for plant, the results may be additive effect ofcopper and boron.

Example 5 Preparation of Boric Acid Coated Nanoparticle FertilizersUsing Gold Chloride as the Metal Salt

Gold-boric acid (Au—B) nanostructures were prepared in aqueous medium byreduction synthesis method. Gold chloride (Au₂Cl₆) was heated in anaqueous medium and added to sodium borohydride. The reaction wasstabilized by adding polyethylene glycol (PEG) to synthesize Au—Bnanoparticles.

The present disclosure is not to be limited in terms of the particularembodiments described in this application, which are intended asillustrations of various aspects. Many modifications and variations canbe made without departing from its spirit and scope, as will be apparentto those skilled in the art. Functionally equivalent methods andapparatuses within the scope of the disclosure, in addition to thoseenumerated in this document, will be apparent to those skilled in theart from the foregoing descriptions. Such modifications and variationsare intended to fall within the scope of the appended claims. Thepresent disclosure includes the full scope of equivalents to which theclaims are entitled. It is to be understood that this disclosure is notlimited to particular methods, reagents, compounds, compositions orbiological systems, which can, of course, vary. It is also to beunderstood that the terminology used in this document is for the purposeof describing particular embodiments only, and is not intended to belimiting.

With respect to the use of substantially any plural and/or singularterms in this document, those having skill in the art can translate fromthe plural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth in this documentfor sake of clarity.

It will be understood by those within the art that, in general, termsused in this document, and especially in the appended claims (e.g.,bodies of the appended claims) are generally intended as “open” terms(e.g., the term “including” should be interpreted as “including but notlimited to,” the term “having” should be interpreted as “having atleast,” the term “includes” should be interpreted as “includes but isnot limited to,” etc.). It will be further understood by those withinthe art that if a specific number of an introduced claim recitation isintended, such an intent will be explicitly recited in the claim, and inthe absence of such recitation no such intent is present. For example,as an aid to understanding, the following appended claims may containusage of the introductory phrases “at least one” and “one or more” tointroduce claim recitations. However, the use of such phrases should notbe construed to imply that the introduction of a claim recitation by theindefinite articles “a” or “an” limits any particular claim containingsuch introduced claim recitation to embodiments containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should be interpreted to mean “at least one”or “one or more”); the same holds true for the use of definite articlesused to introduce claim recitations. In addition, even if a specificnumber of an introduced claim recitation is explicitly recited, thoseskilled in the art will recognize that such recitation should beinterpreted to mean at least the recited number (e.g., the barerecitation of “two recitations,” without other modifiers, means at leasttwo recitations, or two or more recitations). Furthermore, in thoseinstances where a convention analogous to “at least one of A, B, and C,etc.” is used, in general such a construction is intended in the senseone having skill in the art would understand the convention (e.g., “asystem having at least one of A, B, and C” would include but not belimited to systems that have A alone, B alone, C alone, A and Btogether, A and C together, B and C together, and/or A, B, and Ctogether, etc.). It will be further understood by those within the artthat virtually any disjunctive word and/or phrase presenting two or morealternative terms, whether in the description, claims, or drawings,should be understood to contemplate the possibilities of including oneof the terms, either of the terms, or both terms. For example, thephrase “A or B” will be understood to include the possibilities of “A”or “B” or “A and B.”

In addition, where features or aspects of the disclosure are describedin terms of Markush groups, those skilled in the art will recognize thatthe disclosure is also thereby described in terms of any individualmember or subgroup of members of the Markush group.

As will be understood by one skilled in the art, for any and allpurposes, such as in terms of providing a written description, allranges disclosed in this document also encompass any and all possiblesubranges and combinations of subranges thereof. Any listed range can beeasily recognized as sufficiently describing and enabling the same rangebeing broken down into at least equal halves, thirds, quarters, fifths,tenths, etc. As a non-limiting example, each range discussed in thisdocument can be readily broken down into a lower third, middle third andupper third, etc. As will also be understood by one skilled in the artall language such as “up to,” “at least,” and the like include thenumber recited and refer to ranges which can be subsequently broken downinto subranges as discussed above. Finally, as will be understood by oneskilled in the art, a range includes each individual member. Thus, forexample, a group having 1-3 bonds refers to groups having 1, 2, or 3bonds. Similarly, a group having 1-5 bonds refers to groups having 1, 2,3, 4, or 5 bonds, and so forth.

From the foregoing, it will be appreciated that various embodiments ofthe present disclosure have been described in this document for purposesof illustration, and that various modifications may be made withoutdeparting from the scope and spirit of the present disclosure.Accordingly, the various embodiments disclosed in this document are notintended to be limiting, with the true scope and spirit being indicatedby the following claims.

What is claimed is:
 1. A nanofertilizer comprising a metal nanoparticlecoated with boric acid, wherein the metal nanoparticle is selected fromthe group consisting of gold, copper, aluminum, nickel, chromium, iron,cobalt, tin, titanium, zinc, lead, platinum, palladium, rhodium,tantalum, ruthenium, tungsten, an alloy thereof, and a combinationthereof.
 2. The nanofertilizer of claim 1, wherein the boric acid ispresent in the amount of about 0.001 ppm to about 2.0 ppm of the totalweight of the nanofertilizer.
 3. The nanofertilizer of claim 1, whereinthe ratio of boric acid to metal is from about 1:2 to about 2:1 w/w. 4.The nanofertilizer of claim 1, wherein the size of the metalnanoparticle is in the range of 10-1000 nanometers.
 5. Thenanofertilizer of claim 1, wherein the nanofertilizer is in an aqueoussolution.
 6. A nanofertilizer comprising at least one plant nutrientcoated on a metal nanoparticle, wherein the at least one plant nutrientis selected from the group consisting of potassium nitrate, calciumnitrate, magnesium nitrate, ammonium phosphate, magnesium sulfate,potassium phosphate, calcium carbonate, ammonium nitrate sulfate,ammonium thiosulfate, aqua ammonia, urea, sodium nitrate, potassiumcarbonate, potassium chloride, potassium magnesium sulfate, potassiummetaphosphate, zinc phosphate, zinc ammonium phosphate, zinc sulfate,manganese sulfate, manganese ammonium phosphate, ferrous ammoniumsulfate, ferrous ammonium phosphate, cupric ammonium phosphate, coppersulfate, ammonium molybdate, sodium molybdate, molybdenum sulfide, and acombination thereof.
 7. The nanofertilizer of claim 6, wherein the metalnanoparticle is selected from the group consisting of gold, silver,copper, aluminum, nickel, chromium, iron, cobalt, tin, titanium, zinc,lead, platinum, palladium, rhodium, tantalum, ruthenium, tungsten, analloy thereof, and a combination thereof.
 8. The nanofertilizer of claim6, wherein the size of the metal nanoparticle is in the range of 10-1000nanometers.
 9. The nanofertilizer of claim 6, wherein the nanofertilizeris in an aqueous solution.
 10. The nanofertilizer of claim 6, whereinthe at least one plant nutrient is present in the amount of about 0.001ppm to about 2.0 ppm of the total weight of the nanofertilizer.
 11. Amethod of making a nanofertilizer comprising a metal nanoparticle coatedwith a plant nutrient, the method comprising: providing a metalnanoparticle or salt thereof; and coating the metal nanoparticle with atleast one plant nutrient or precursor thereof, wherein the at least oneplant nutrient is selected from the group consisting of boric acid,disodium octaborate tetrahydrate, calcium borate, magnesium borate,sodium borosilicate, sodium tetraborate decahydrate, sodium borate,sodium tetraborate, disodium tetraborate, chloride, lime, gypsum,superphosphate, iron sulfate, iron chelate, ferritin, zinc oxide, zincsulfate, zinc chelate, potassium nitrate, calcium nitrate, magnesiumnitrate, monoammonium phosphate, ammonium sulfate, magnesium sulfate,monopotassium phosphate, calcium carbonate, ammonium nitrate sulfate,ammonium thiosulfate, aqua ammonia, calcium cyanamid, crotonylidenediurea, diacyandiamide, isobutylidene diurea, sodium nitrate, potassiumcarbonate, potassium chloride, potassium magnesium sulfate, potassiummetaphosphate, potassium sulfate, calcium chloride, calcium oxide,calcitic limestone, dolomitic limestone, magnesium ammonium phosphate,magnesium oxide, copper chelates, cupric ammonium phosphate, coppersulfate, copper frits, copper polyflavonoid, malachite, azurite, cuprousoxide, cupric oxide, cupric acetate, boron frit, ferric sulfate, ferroussulfate, ferrous ammonium sulfate, ferrous ammonium phosphate, ferrousoxalate, ferrous carbonate, iron chelate, iron lignosulfonate, ironpolyflavonoid, iron frits, iron methoxyphenylpropane, ferrous oxide,ferric oxide, iron ammonium polyphosphate, manganese oxide, manganesemethoxyphenyl propane, manganese frits, manganese chloride, manganesecarbonate, manganese sulfate, manganese chelate, manganese ammoniumphosphate, manganese polyflavonoid, ammonium molybdate, sodiummolybdate, molybdenum frit, molybdenum trioxide, molybdenum sulfide,zinc fit, zinc carbonate, zinc phosphate, zinc ammonium phosphate, zincsulfide, zinc lignosulfonate, zinc polyflavonoid, and a combinationthereof.
 12. The method of claim 11, wherein providing the metalnanoparticle or salt thereof comprises providing the metal nanoparticleselected from the group consisting of gold, silver, copper, aluminum,nickel, chromium, iron, cobalt, tin, titanium, silicon, zinc, lead,platinum, palladium, rhodium, tantalum, ruthenium, tungsten, an alloythereof or a combination thereof.
 13. The method of claim 11, whereinproviding the metal nanoparticle or salt thereof comprises providing themetal salt selected from the group consisting of a metal chloride, ametal fluoride, a metal acetate, a metal sulfate, a metal nitrate, ametal carbonate, a metal nitrite, a metal citrate, a metal cyanide, ametal hydroxide, a metal oxide, a metal phosphate, and a combinationthereof, and the plant nutrient in the aqueous medium.
 14. The method ofclaim 11, wherein providing the metal nanoparticle comprises forming themetal nanoparticle through salt reduction synthesis, reverse micellesprocess, microwave dielectric heating reduction, ultrasonic irradiation,radiolysis, solvothermal synthesis, bioreduction, heat evaporation,photochemical reduction, electrochemical synthesis, or a combinationthereof.
 15. The method of claim 11, wherein coating the metalnanoparticle with the at least one plant nutrient or precursor thereofcomprises: mixing the metal nanoparticle or salt thereof and the atleast one plant nutrient in an aqueous medium to form a solution; andadding a reducing agent to the solution to form the coated metalnanoparticle.
 16. The method of claim 15, wherein mixing the metalnanoparticle or salt thereof and the plant nutrient in the aqueousmedium to form the solution comprises heating the solution at atemperature of about 70° C. to about 110° C.
 17. The method of claim 15,wherein adding the reducing agent to the solution comprises adding thereducing agent selected from the group consisting of sodium citrate,sodium borohydride, hydroquinone, glycol ethylene, formaldehyde,ethanol, hydroxyl radicals, sugar pyrolysis radicals, hydrazine hydrate,saccharide, N,N-dimethylformamide, and a combination thereof, to thesolution.
 18. The method of claim 15, wherein adding the reducing agentto the solution comprises heating the solution at a temperature of about70° C. to about 110° C.
 19. The method of claim 15, further comprisingadding a stabilizer to the solution after adding the reducing agent. 20.The method of claim 19, wherein adding the stabilizer comprises addingthe stabilizer selected from the group consisting of polyvinyl alcohol,polyethylene glycol, carboxymethyl cellulose, poly(vinylpyrrolidone),sodium dodecyl sulphate, long-chain thiol, long-chain amines, carboxyliccompounds, bovine serum albumin, cellulose, and a combination thereof,to the solution.
 21. The method of claim 19, further comprising mixingthe solution to allow the temperature of the solution to decrease toroom temperature.